[Bug] --zero concatenates entries instead of writing NUL separators

[equationzhao]

Describe the bug
--zero is documented as ending each output line with NUL. It currently concatenates entries without any delimiter.

To Reproduce

1. Build the current repository:

go build -o /tmp/g-bug-audit .

2. Create two files:

tmp=$(mktemp -d)
touch "$tmp/a" "$tmp/b"

3. Inspect the output bytes:

/tmp/g-bug-audit --no-config --disable-index --classic -A --zero "$tmp" | od -An -tx1c
printf 'exit=%s tmp=%s\n' ${pipestatus[1]:-${PIPESTATUS[0]}} "$tmp"

4. Actual output:

           61  62
           a   b

exit=0 tmp=/var/folders/1b/57vdxmgj7s1glqm6tbsw1frm0000gn/T/tmp.o9IEbAMyXW

5. Expected output: the byte stream should contain 61 00 62 00 or at least a NUL after each entry.

Screenshots
Not applicable.

Info (please complete the following information):

• OS: macOS darwin/arm64
• Version: v0.31.2, Go go1.26.1

Additional context
The zero-output printer appears to write each entry's content but never writes \x00.